1. Field of the Invention
This invention relates to a method of manufacturing a semiconductor device, to an acid etching resistance material, and to a copolymer.
2. Description of the Related Art
A compound semiconductor to be employed for constituting a light emitting element is generally very high in refractive index, so that most light emitting elements suffer loss of light due to the reflection of light at the surface or interface thereof. Therefore, it has been difficult to externally retrieve the light that has been generated inside the light emitting elements at a high efficiency. In the case of compounds such as gallium phosphide, the refractive index thereof is as high as 3.5 or so, so that because of the total reflection thereof, only 19% of incident light can be taken out. To cope with this problem, it is usual conducted to form, as an antireflection layer, a monolayer film having a refractive index of about 1.5 on the surface of a light emitting element. However, since the difference in refractive index between the light-emitting surface and the monolayer film is relatively large, the light emitting element constructed as described above is still insufficient to overcome the aforementioned problem.
As a measure for enhancing the light extracting efficiency, there is known a method wherein the surface of light emitting element is roughened to increase the surface area of the light emitting element, thus enhancing the external quantum yield. The roughening of the surface of light emitting element can be generally performed by surface treatment using an etching solution comprising hydrochloric acid, sulfuric acid, hydrofluoric acid, hydrogen peroxide or a mixture thereof. In this case, since a specific crystal face of compound semiconductor corrades when the compound semiconductor is subjected to wet etching, a pattern of triangular pyramid-like configuration having a size of the order of μm would be formed depending on crystal face. As a result, the surface area of the light emitting element is increased, resulting in an increase of the light extracting efficiency and hence the enhancement of luminance.
The surface-roughening treatment by this chemical etching is called a “frosting treatment” and can be executed by a very simple technique, i.e., by simply dipping a compound semiconductor in an etching solution. More specifically, this frosting treatment is performed with the entire surfaces of the compound semiconductor substrate, excluding the surface where the roughening is taken place, being covered with a protecting film so as to prevent the electrodes, for instance, from being contacted with etching solution. The protecting film to be employed herein is required to be such that it can be easily removed after finishing the frosting treatment and at the same time, it is resistive to the etching solution. However, no one has succeeded as yet to obtain a material having such characteristics as described above.
Meanwhile, there is known an optical pattern etching method which is a fine fabrication technique for etching a substrate so as to form an optical pattern on the surface thereof, this optical pattern etching method comprising a step of coating a photosensitive hydrofluoric acid etching resist material on the substrate, a step of exposure, a step of development, and a step of etching. This optical pattern etching method is one of elemental techniques to be employed in the manufacture of a large-scale integrated circuit (LSI) substrate and is also applied to the manufacture of a micro-electromechanical system (MEMS) of optical scanning apparatus, and the manufacture of semiconductor devices such as a light-emitting diode (LED) in recent years.
In particular, the etching step using hydrofluoric acid in the aforementioned optical pattern etching method is expected to be applicable to the etching of a sacrificial layer of an optical scanning apparatus having a movable element structure and provided with an optical waveguide which is low in hydrofluoric acid resistance, or to the frosting treatment of LED for enhancing the light extracting efficiency through the roughening of the surface of light emitting element made from a compound semiconductor. In this case, in order to shorten the running time of the manufacturing method, it is desirable to employ concentrated hydrofluoric acid (for example 49%) in the etching step.
However, the manufacture of an LSI substrate is mainly performed by etching using dilute hydrofluoric acid due to the facts that the conventional photo-sensitive etching material that has been developed for the manufacture of LSI substrate is poor in resistance to hydrofluoric acid and that a photosensitive hydrofluoric acid etching resist material to which concentrated hydrofluoric acid can be applicable is not yet available. Accordingly, if concentrated hydrofluoric acid etching is to be performed, the portions which are made of a material poor in hydrofluoric acid resistance are required to be formed after finishing the step of hydrofluoric acid etching, thus raising problems that the manufacturing process is complicated and the manufacturing period is prolonged.